A micro-mixer is produced, for example, by machining a semiconductor substrate of Si or the like employing a micro-machining technique.
In a micro-mixer of this type, for example, two kinds of liquids (fluids) A, B are combined to form a two-layer laminar flow (A+B), and then the laminar flow (A+B) is divided into two half-flows (A+B)/2 along the direction of the laminar flow. Then, two half-flows (A/2+B/2) are combined to form a four-layer laminar flow (A/2+B/2+A/2+B/2), and then this laminar flow is divided in two along the direction of the laminar flow. By repeating combining of laminar flows and dividing of a laminar flow along its direction this way, the liquids A, B are gradually divided into smaller layers, so that the liquids A, B are diffused faster.
However, in conventional micro-mixers, passages for combining and dividing fluids (liquids) are minute and require high production accuracy. Hence, the method of machining (producing) them is complicated. Further, accurate alignment is required, which leads to high production cost. Further, since the passages are minute, they easily become clogged with liquid particles when they have complicated passage structure. Clogging occurs easily especially at narrow slits provided for dividing fluids. Another problem is that flows of fluids become uneven, which makes it difficult to obtain the required mixing performance.